This application requests funds to purchase a Cytomation MoFlo MLS2000 high performance flow cytometer. This instrument will be configured with three lasers on a standard optical bench, an aerosol containment device, and a high resolution cell deposition unit. The MoFlo will be the foundation of a new cell sorting core facility within the Alvin J. Siteman Cancer Center at Washington University. The users identified in this proposal, all established NIH-funded scientists with significant cytometry expertise, will account for 80% of usage. The remaining hours will be allocated to other investigators at Washington University, with priority given to members of the Siteman Cancer Center. There are currently no high-speed cell sorters available at Washington University or the nearby campus of St. Louis University Health Sciences Center. This instrument will greatly benefit the key personnel, whose diverse research interests include hematopoiesis and progenitor mobilization, molecular mechanisms of leukemogenesis, herpes viral latency, T cell development and activation, graft-versushost disease, and the immune response after solid organ transplantation. In addition, there will be significant dividends for the Siteman Cancer Center (whose membership was awarded $76.2 million in direct costs for cancer-related research from the NIH in FY 2000) and the Washington University scientific community at large. The core facility will be directly supervised by the P.I. and staffed by an experienced, full-time technician. The funds requested are for purchase of the MoFlo only. The startup and operational costs of the cell sorting core facility will be provided by this institution and offset by user fees. An advisory committee will oversee management of the cell sorter and ensure its long-term stability as a resource for the medical school.